class Solution {
public:
    void sortColors(vector<int>& nums) {
        int left = -1, i = 0, right = nums.size();
        while(i < right)
        {
            if(nums[i] == 0)
                swap(nums[++left], nums[i++]);
            else if(nums[i] == 1)
                ++i;
            else // == 2
                swap(nums[--right], nums[i]);
        }
    }
};